Telephone-exchange system.



No. 793,972. PATEN'JI'ED JULY 4, 1905. H. Ch WEBSTER TELEPHONE EXCHANGE SYSTEM".

APPLIOATION FILED mm. 25, 1903.

WET 11555125 m l lo. 793.972,

i Satellite Patented July 4t, 1902).

ii El ie (JARLSON TllELlDl lilONE .iilAN UliACllUltlNH COMPANY,

t l l? hOU lllCSlll lh,

NEW" YORK, A tiORPtl ltAilllUlii OF NlGrV YORK.

SPECIFICATION forming part of Letters Patent 1J0. 793,972, dated July 4:, 1905.

Application filed March 25, 1903. Serial No. 149,559.

To (Iii/1 when it may con/(Bernhllie it known that I, l lanai (El. 'lticns'rnu, a citizen of the United States, residing at Uhicage, in the county of (look and t ltate of illinois, have invented a certain new and useful .lniprovement in 'lelephone-Exchange Systems, of which the Following is a full, clear, concise, and eXact description, reference being bad to the accompanying drawing, forming a part of this specification.

My invention relates to telephone-exchange systems, and more particularly to the socalled testcircuit for use in connection therewith.

My invention is particularly well adapted for use in connection with telephone systems in which a source of current located at the central exchange is utilized for the purpose of supplying talking and signaling currents to the subscribers substation apparatus. it has been the common practice to provide each line connected with a multiple-switchboard exchange with a plurality of spring-jacks, one for each section of the multiple switchboard. Test contacts or thimbles of the jacks associated with any one line have been so connected with the circuits of the system that the insertion of a plug of an operators cordcircuit at any one of the operators positions causes some change in the potential value of the test-thimbles associated with the same line. A test-contact, which has usually been the tip-contact of the operators plug, when applied to a test-thimble of a busy line, has caused the closure of an electrical circuit, thereby producing a click in the operators telephone-receiver to indicate the busy condition of the tested line. Under normal conditions, in which the tested line is not in use, the associated test-thimbles are either electrically insulated from the remainder of the system or are maintained at a potential equal to that ol? the tip of the testing-plug. The insertion of a plug within a jack has caused a considerable change in the potential of the test-thimbles, whereby an unduly loud click is pro d need in the subscribers receiver due to the the system, whereby the application ol the tip-contact of a testing-plug does not affect the operatofls telephone, set to cause a busytest signal. The means which I prefer to em ploy for the purpose of obtaining the desired potential of the testing tip-contact may be described as a resistance permanently connected between the poles ol the common source of 5 current and to some intermediate point in which the testing tip-contact is connected at the time of making a busy test.

While my invention may be applied to a great variety of telephone systems, I shall de- 7 scribe it as applied to a differential relay system such as that illustrated in the accompanying drawing.

At each of the substations A and B, I have illustrated the usual form of apparatus in which a receiver'hook 1 when in its normal depressed position, due to the weight of the receiver 2, connects between the line-limbs 3 and 4 the call -bell 5 and the condenser 6. When in its upper position, due to the removal of the receiver 2, the switch-hook ll closes circuit between the line-limbs 3 and 4: through the transmitter 7 and the primary 8 of an induction-coil, whose secondary 9 is serially connected with the receiver 2. The 5 line-limb 3, extending to each of the substations, leads to the central exchange 0, where it is connected with the grounded positive terminal of the common battery 10 through a winding 11 of the dill'erential cut-otl' relay 12. 9

there being included in this circuit the armature of the differential cut-off relay, this armature normally closing a connection through the back contact 16. A front contact 17 for this armature 15 is connected with the sleevecontacts 18 of the line-jacks 19, whose tip-contacts 20 are permanently connected with the limb 3 of the telephone-line, as shown. The sleeve-contacts 18, as will be hereinafter more fully explained, also form the test-thimbles of the spring-jacks. The operators cord-circuit comprises an answering-plug 21 and a calling-plug 22, whose tip-contacts are connected through the tip-strand 23 and whose sleevecontacts are connected by the sleeve-strand 24.

The usual operators ringing and listening key 25 is provided, the manipulation of this key in one direction serving to connect the operators telephone set 26 in bridge of the cord-strands. The manipulation of this key also serves to break the continuity of the tip-strand, the condenser 27 being then included in the tipstrand circuit. The sleeve-strand includes in its circuit the supervisory relays 28 and 29, which are respectively shunted by condensers 30 and 31. The common terminal of the supervisory relays is connected, through an impedance-coil 32, with the negative pole of the common battery 10. The armatures 33 and 34 directly control the continuity of circuits through the supervisory signal-lamps 35 and 36, the operation of these lamps being dependent upon the connection with the contact 37 of the armature 38 of the supervisory controlling-relay 39, which is connected between the negative pole of the battery 10 and the tip-strand 23 of the operators cord-circuit. A manipulation of the ringing-key serves to connect the calling-generator 40 in bridge of the cord-circuit. A conductor 41 then serves to connect the tip-strand 23, leading to the calling-plug 22, with the negative pole of the battery. A condenser 42 is included in the operators telephone-circuit, which a manipulation of the listening-key serves to connect in bridge of the cord-circuit. Preferably permanently connected between the terminals of the common battery 10 are the resistances 43 and 44, which may be respectively of four hundred and fifty and five hundred ohms resistance. The common terminal of the resistances 43 and 44 is connected, through an impedance-coil45, with the contact 46. In order to balance the operators telephone-circuit to prevent noise due to inductive disturbances, I connect the impedance-coil 47 between the telephone-circuit and the grounded side of the battery 10. The resistances 43 and 44 may be looked upon as a single resistance to an intermediate point, between the terminals of which a connection is made with the tipstrand of the cord-circuit leading to the testcontact or tip-contact of the calling-plug.

The operation of the system described is as follows: The removal of the receiver atsubstation A from its switch-hook 1 causes the closure of a circuit from the battery 10 through the line-relay 13 and the two differential windings of the cutotf relay 12. On account of the differential relation of these windings of the cutoff relay no net energization thereof is produced, and its armature 15 is therefore not attracted. The line-relay 13 being energized, however, causes a visual signal, which the operator answers by the insertion of the plug 21 of her cord connecting apparatus within one of the line-jacks associated with the line leading to substation A. The insertion of this plug within a jack, as shown, causes a closure of the circuit, which may be traced as follows: from the negative pole of the battery 10 through the supervisory controlling-relay 39, the tip-strand of the cord connecting apparatus, the tip-contact of the plug 21, the tipspring 20 of the line-jack, the winding 11 of the difierential cut-off relay 12 to the positive pole of the battery. The closure of this circuit of decreased resistance through the winding 11 of the cut-off relay causes a net energization thereof, whereupon its armature 15 is attracted into the position shown. The attraction of this armature causes a break in the otherwise continuous circuit from the negative pole of the battery 10 through the line-relay and the winding 14 of the differential cut-ofi' relay to the substation A. At the same time the attraction of the armature 15 connects the limb 4, leading to the callingsubstation, directly with the sleevesprings and test-thimbles 18 of the associated linejacks 19. A circuit from the battery 10 may be traced through the substation-transmitter as follows: from the positive pole of the battery 10 through the winding 11 of the difierential cut-off relay, through line limb 3, switch-hook 1, primary Winding 8, transmitter 7, line-limb 4, armature 15, contact 17, sleeve-spring 18, sleeve-strand 24 of the cordcircuit, the winding of the supervisory relay 28, and the impedance-coil 32 to the negative pole of the battery 10. The closure of this circuit causes the attraction of the armature 33 of the supervisory relay 28, whereupon the otherwise-completed local circuit through the supervisory signal-lamp 35 is broken. Upon the insertion of the answering-plug 21 within a line-jack 19 acircuit is established through the supervisory signal-lamp 36 on account of the attraction of the armature 38, the supervisory relay 29 not being energized to cause the attraction of its armature 34. The operator manipulates her listening-key and ascertains the number of the substation with which the calling subscriber desires connect-ion. Learning that the substation B is desired, the operator applies the tip-contact of her callingplug 22 to one of the test-thimbles 18 of the line-jacks associated with the telephone-line to substation B. If the line is not in use and the armature 15 of the differential cut-01f reveae're lay conseipiently not attracted, the test-thinlbles will be insulated from other parts ol the telephone system, and the application ol the test-contact of the calling-plug will .ause no change in the potential of the ti p-straml associated therewith, nor will a closed electric circuit be established to cause a click in the operators receiver. ll, on the other hand, the line leading to substation ii is already in use, the test-thimbles 1c 01 the associated jacks will have been connected, through the sleevc strand 2a and the supervisory relay 2S) and the impedance-coil 32, with the negative pole ot' the battery 10. clincc the tip-contact when making a test is connected, through the inn pedance-coil 45, with a point in a high-resistance circuit iliitermediate between the terminals ot the common battery 10, the potential o'l this ti p-contact is intermediate between that of the terminals of the battery 10, the potential of the tip'contact being dependent. upon the relative resistances of the resistances 43 and a l. The potential of the testing tip contact being dil'lcrcnt, therefore, from that of a test-thimble of a busy line, a current is caused to tlow which produces in partial charge or discharge oil? the condenser 42, whereby the click produced in the opcratofis receiver. Upon the removal of the receiver at substation B from its switch-hook a circuit is conr pletcd through the impedance-coil 32, the supervisory relay 529, the sleeve-straiul 24, the test-thimble 18, the contact 17, the armature 15, the transmitter 7, the primary winding 8, the switclrhook l, the line-limb 2-3, the wind ing 11 ol the differential cut-oli relay, and the battery 10. The test-thimbles 18, being connected to this circuit, are charged to a potential in termediate between the potentials of the positive and negative terminals of the common battery 10. The resistances a3 and H are made relatively such that the potential of a testing tip-contact 01. a calling-plug will be only slightly different from that of the testthiinbles 18 of a busy line in which a closed circuit such as that previously described through the substation -telcphone amiaratus has been completed. On account of this rela tively small difi'erence between the potentials ol? the tip-contact and the tcst-thimble the disturbance or click produced in the sul scribers receiver may be made comparatively insignificant, whereby the annoyance due to the excessively loud click produced in systems of the prior art is avoided. After having made a busy test, as described, to ascertain whether or not the line leading to substation B is busy the operator upon lcari'iing that this line is not in use inserts her calling-plug 22 within one of the line-jacks l9 and manipulates her ringing-key to connect the ringing generator in bridge of the cord-strands leading to the c: lled line. llheinsertionol the calling plug within a line-jack 19 at once causes the closure et a circuit through the wnuling ll ol the dillerei'itial cut-oil relay, whereby the same is energized to cause the attracticm ol the armature 15, whereby the QlPUVQ-GOI'I- tacts its are connected directly with the limb *1; ot the called line, and whereby the connection between the limb 4: through the (lillerential relay-wimling 1a and the linerelay l?) with. the negative pole of the battery '10 is broken. in order that the interruption in the circuit throi'igh the dil'li'eren ti al relay-winding l1, due to the manipulation oi the ringing-key, may not break the circuit through this winding '1 l to cause the retraction ol the armature 15, the conductor l-fl is provided, whereby upon the manipulation of the ringing-key a circuit may be traced through the conductor -l-l lrom the negative pole of the battery and the ti p-straiul of the corthcircuit through the winding 11 l. of the dill'ercntial cut-otl relay to the positive pole of the battery in. Tllhusthearniature is retained in its attracted position to permit the ringii1g-current to pass from the sleevestrand 2%; through the (jOlllltLCli i7 and armature if) to the line-limb 4., leading to substation B. in answering the calling-signal the subscriber at substation .l-i removes his rcceiver 52 from the switch-hook '1, thereby causing the closure of a circuit through the snpervisory relay 29, whereby the same is encrgizcd to cause the attraction of its arn'iature Bel, whereupon the previously-coinplcted circuit through the si'ipervisory signaling-lann 36 is interrupted to cause its extinction. The connected subscribers having completed their coi'lvcrsatioll, the replacement of either of the receivers upon its switch-hook causes an interruption in the continuity of the circuit through the associated supervisory relay 28 or 29. The consequent (lecnergization of a su iervisory relay causes the retraction of the associated armature, whereby the su 'iervisory signaling-lamp is caused to glow, thereby no ti'lying the operator that the connected subscriber has finished his conversation. The operate r therel'u'mn removes the cord-connecting plugs from the jacks, whereby the circuit through the siu'iervisory controlling-relay 39 is broken, and the armature 2-38 is retracted to cause a break in the circuit supplying current to the supervisory signalirig-lamps. The removal of the coI'd-connecting plugs trom the line-jacks also causes the deenergization ol? the CUlJ'OIl'l relays, whereu 'ion the arinatures 15 are retracted into their normal position.

l t has heretofore been attenuated to reduce the click in a subscribcfis telephone-receiver upon testing a busy line by introducing resistance into the test-circuitor otherwise cutting down the flow of current upon making a test. I have found that the reduction of this disagrcealiilc click is much more ellectively attained by the provision oi means whereby the dillerence in potential between the test-contact and the test-thimble is made com 'iaratively small. in the system herein described the potential of the test-thimble of a busy line on which the receiver has been removed from its hook is never less than a certain limiting minimum value dependent upon the relative resistances of the relay and impedance windings in the circuit. The potential may be somewhat greater than this minimum value, an amount dependent upon the resistance in the line-circuit. With metallic lines of ordinary length this limiting minimum value of the potential of the test-thimble of a busy line is never very greatly exceeded. In accordance with my invention I provide means whereby the potential of the test-contact be fore making a test connection is charged to a potential preferably slightly lower than the limiting minimum potential of the testthim ble. In practice]. [ind it desirable where the limiting minimum potential of the test-thimble is twenty volts above that of the earth to make the potential of a testing-contact approximately eighteen or nineteen volts.

I have shown but one means of charging the testing tip-contact to a potential intermediate between the potentials of the terminals of the common battery. Many other wellknown means for accomplishing this result may of course be equally well QU'IPlQYQd.

Vhile I have herein shown and described my invention, which pertalns particularly to the improved testing-circuit as applied to one telephone system, it will be apparent that my invention may be applied to other systems with ClOSllZtblG results, and I do not, therefore, wish to limit myself to the precise disclosure herein set forth; but,

Having described my invention, I claim as new and desire to secure by Letters Patent 1. In a tele 'ihone-exchange system, the combination with a telephoneline extending by its limbs from a substation to an exchange, of a source of current at the exchange, a testthimble associated with said line, cord connecting apparatus at the central exchange, means whereby the connection of said cord connecting apparatus with said line causes a change in the potential of said test-thimble, a test-contact associated with said cord connecting apparatus, two slightly difierent high resistances permanently serially connected between the terminals of said source of current, means for connecting said test-contact to a point between said resistances, and a signaling device adapted upon application of the charged test-contact to the test-thimble to indicate the condition of the tested line.

2. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange, a testthimble associated with said line, cord conmeans whereby the connection of said cord connecting apparatus with said line causes a change in the potential of said test-thimble, l

' a test-contact associated with said cord connecting apparatus, two slightly diflerent high resistances permanently serially connected between the terminals of said source of current, means for connecting said test-contact to a point between said resistances, and an operators telephone set inductively associated with the test-circuit whereby a click is produced in the operators receiver upon the application of the charged test-contact to the test-thimble of a busy line.

3. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange, a testthimble associated with said line, cord connecting apparatus, means whereby the connection of said cord connecting apparatus with said line causes a slight change in the potential of said test-thimble, a high resistance permanently connected between the terminals of said source of current, a test-contact for said cord connecting apparatus, means for connecting said test-contact to an intermediate point in said resistance such that the test-contact is charged to a potential only slightly different from the potential of the test-thimble of a busy line, and a signaling device adapted upon application of the charged testcontact to the test-thin'iblc to indicate the condition of the tested line.

at. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange, a test thimble associated with said line, cord connecting apparatus at the exchange, means whereby the connection of said cord connecting apparatus with a line having a circuit through a transmitter at a substation causes the test-thimble to be charged to a potential equal to or greater than a certain potential intermediate between the potentials of the terminals of said source of current, a high resistance permanently connected between the terminals of said source of current, a test'contact connected to an intermediate point in said resistance such that the test-contact will be charged to a potential only slightly different from the potential of the test-thimble of a busy line and a signaling device adapted upon application of the charged test-contact to the test-thimble to indicate the condition of the tested line.

5. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from asubstation to an exchange, of a source of current at the exchange for supplying talking and signaling currents to said line, a test-thimble associated with said line, cord connecting apparatus at the exchange for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes a change in the potential of said testthimble, two slightly ditle'rent resistances permanently serially connected between the terminals of said source of current, a teslrcontact connected to a point between said resistances, and a signaling device adapted upon application of the charged test-contact to the 'test-thimhle to indicate the condition ol the tested line.

6. in a tele ihone-exchangc system, the combination with a telephone line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying talking and signaling currents to said line, a test-thimble associated with said line, cord connecting apparatus at the exchange for connecting said line with another For conversation, means whereby the connection of said cord connecting apparatus with said line causes a change in the potential of said testthimble, two slightly ditlerent resistances permanently serially connected between the terminals of said source of current, a test-contact connected to a point between said resistances, and an open'ators telephone set inductively associated with the test-circuit whereby a click is produced in the operators receiver upon the application of the charged test-contact to the test-thimble of a busy line.

7. in a telephonc-excl1ange system, the combination with a telephone-line extemling by its limbs from a substation to an exchal'lge, of a source of current at the exchange. For supplying talking and signaling currents to said line, a test-thimble associated with said line, cord connecting apparatus at the exchange for connecting said line with another forconversation, means whereby the connection of said cord connecting apparatus with said line causes a change in the potential ol said testthinible, a resistance permanently connected between the terminals of said source of current, a test-contact connected to an intermediate point in said resistance such that the test-contact is charged to a potential only slightly diti'erent from the potential of the tcst-thimble of a busy line, and a signaling device adapted upon application of the charged test-contact to the test-thimble to indicate the condition of the tested line.

8. in a telephone-exchange system, the combination with atele 'Jhone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying talking and signaling currents to said line, a test-thimble associated with said line, cord connecting apparatus at the exchange for conl'iecting said line with another for convera tion, means whereby the connection of said cord connecting apparatus with a line having a circuit through a transmitter at a substation causes the test-thimble to be charged to a potential equal to or greater than a certain potential intermediate between the potentials of the terminals of said source of current, a resistance permanently connected between the terminals of said source oi" current, a test-contact connected to an intermediate point in said resistance such that the test-contact will be charged to a potential only slightly different from the potential of the test-thimblc of a busy line, and a signaling device adapted upon application of the charged test-contact to the test-thimble to indicate the condition of the tested line.

9. in a telephone-exchange system, the combination with a telephonc-line extending by its limbs from a substation to an exchange, of a source 01'' current at the exchange for supplying talking and signaling currents to said line, a tcst-thimble associated with said line, cord connecting apparatus at the exchange for conneeting said line with another for conversation, means whereby the connection of said cord connecting apparatijis with a line having a circuit through a transmitter at a substation causes the test-thimldc to be charged to a potential equal to or greater than a certain potential intermediate between the potentials of the terminals of said source of current, a high resistance included in a circuit between the terminals and source of current, a test-eon tact associated with said cord connecting apparatus connected through an im 'iedancc-coil to an interm cdiate point in said resistance such that the test-contact will be charged to a potential only slightly ditlercntlrom the potential ot the test-thimlde of a busy line, and an, operators telephone set inductively associated with the test-circuit whereby a click is pro duced in the operators receiver upon the application of the charged test-contact to the test-thimble ot' a busy line.

10. .In a telcphone-exchange system, the combination with a tele iihone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying talking and signaling currents to said line, a test-thimble associated with said line, cord connecting apparatus at the exchange for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with a line having a circuit through a transmitter at a substation causes the testthimble to be charged to a potential equal to or greater than a certain potential intermediate between the potentials ol the terl'ninals of said source of current, a high resistance connected between the terminals of said source of current, a testcontact associated with said cord connecting :uiparatus connected to an intermediate point in said resistance such that the test-contact will be charged to a potential only slightly different from the potential of the test-thiinble of a busy line, and an operators telephone set inductively associated with the test-cireuit whereby a click is produced in the operators receiver upon the ttIJDllGEtlliOli of the charged test-contact to the test-thimble of a busy line,

11. in a telephone-exchange system, the

combination with a telephone-line extending v by its limbs from a substation to an exchange,

of a source of current at the exchange for supplying talking and signaling currents to said line, cord connecting apparatus at the exchange for connecting said line with another for conversation, at test-thimble normally disconnected from said line, but adapted upon the connection of said cord connecting apparatus with said line to be connected with said line, means whereby the connection of said cord connecting apparatus with a line having a conductively-completed circuit through a substation-transmitter causes said test-thim ble to be charged to a potential intermediate between the potentials of the terminals of said source of current, a resistance included in circuit between the terminals of said source of current, a test-contact connected to an intermediate point in said resistance such that the test-contact will be charged to a potential only slightly different from the potential of the test-thimble of a busy line, and an operators telephone set inductively associated with the test-circuit whereby a click is produced in the operators receiver upon the application of the charged test-contact to the testthimble of a busy line.

12. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for l supplying talking and signaling currents to l said line, cord connecting apparatus at the exchange for connecting said line with another for conversation, a test-thimble normally disconnected from said line but adapted upon the connection of said cord connecting apparatus with said line to be connected with said line, means whereby the connection of said cord connecting apparatus with a line having a conductively-completed circuit through a substation-transmitter causes said test-thinlble to be charged to a potential intermediate between the potentials of the terminals of said source of current, a high resistance included in a circuit between the terminals of said source of current, a test-contact associated with said cord connecting apparatus connected through an impedance-coil to an intermedicontact will be charged to a potential only slightly different from the potential of the test-thimble of a busy line, and an operators telephone set associated with the test-circuit whereby a click is produced in the operators receiver upon the application of the charged contact to the test-thimble of a busy line.

In witness whereof I hereunto subscribe my name this 18th day of March, A. D. 1903.

I HARRY Gr. \VEBSTER. lVitnesses:

LYNN A. lVILLIAMs, Jonu STAHR.

ate point in said resistance such that the test- 

